1. Field of the Invention
The present invention relates to an electronic watermark detection device and an electronic watermark detection method and, more particularly, to a method of detecting an electronic watermark inserted into digital images of the MPEG (Moving Picture Experts Group) standard and the like.
2. Description of the Related Art
In recent years, a wide spread of digital satellite broadcasting, Internet distribution, DVD (Digital Versatile Disk) and the like makes digital images be easily delivered to users. Since digital images involve no deterioration of image quality even when copied, protection of their copyright is a crucial issue.
Proposed as a means for realizing protection of copyright of digital images is a technique of adding copyright information etc. at a DCT (Discrete Cosine Transform) coefficient region of a digital image.
Such a device for detecting information in a DCT coefficient is structured as shown in FIG. 12. With reference to FIG. 12, an electronic watermark detection unit 32 receives input of a DCT coefficient and a picture start from a preprocessing unit 31 to detect an electronic watermark inserted into image data (MPEG stream) and outputs a result of the detection and a detection interruption for notifying the result.
Once starting detection of an electronic watermark, the electronic watermark detection unit 32 detects electronic watermarks at constant intervals unless an instruction to stop the detection is given. An interruption processing unit 33 receives input of the detection result and the detection interruption from the electronic watermark detection unit 32 to generate an interruption signal according to a system, as well as outputting the detection result.
In the above-described conventional electronic watermark detection device, since an electronic watermark detection interval is constant and fixed, even with an image whose detection intensity is low, images can be detected only at constant intervals to increase a system load and conversely, with an image whose detection intensity is high, images can be detected only at fixed intervals to delay system control response.